Passive micromixer integration with a microfluidic chip for calcium assay based on the arsenazo III method

The ability for low reagent consumption and minimum waste production in a miniaturised system has generated great interest in the green chemistry field. Herein, a microfluidic system for calcium assays using the arsenazo III method has been developed. The reaction between arsenazo III and calcium to form a blue-purple coloured complex is measured by an embedded miniature fibre optic spectrometer through absorbance increments at 650 nm. A linear range was obtained from 0.2 to 3 mg dL−1 with a detection limit of 0.138 mg dL−1 (S/N=3). The method exhibited good reproducibility based on low and high calcium tests with control serums, the within-run coefficient of variation (CVs) (4.10% and 3.91%), and the run-to-run CV (4.6%) were obtained. The carry-over effect of the method was also 1.98%, which is acceptable for the current system. When compared to a conventional spectrophotometric method, this portable, microfluidic method correlated highly when evaluating serum samples (r 2=0.985; n=15). This similarity suggests that our proposed system could be used for determining the amount of calcium in serum samples.